Secondary timekeeping apparatus



June 6, 1950 n s. JoHNsoN sul.

SECONDARY TIIIEKEEPING APPARA'IUS med 11110, .1946

39N: @was Nass@ B 2 Sheets-Sheet 1 lsb a E 15b lNVENTOR B. dOll/VSON Y C F2 GE/GER Ar'roRNEY June 6, 1950 R. aJOHNsoN ETAL SECONDARY TIMEKEEPING APPARATUS 2 Sheets-Sheet 2 Filed April 10, 1946 n MME m we@ o NJE .w .l A BF.

Y 2-2 of Fig. l;-

Pstented June 6, 1950 v Y :susa: Y sacoNnAaY G Arraaaa'us ma n. Johnson me um F. Gaia, nmvllmntlm, N.' Y., to International Ilsicorporation o! New Yorknees MachineaCorporation. New York, N. Y., a

Application Apr'u 1o, 194s, serial No. 651,12:

6 Claims. (Cl. 58-26) l( This invention relates generally to clocks, and

clock systems, of the type disclosed in U. S. l

patent to Bryce, No. 1,687,491. granted October 16," 1928. and more particularly, this Ainvention has to do withimprovements in secondary clocks. and similar time-keeping apparatus of the type.

which are operated by 'electrical impulses trans mitted at predetermined-time-intervals under the control of a master clock. v

An object of this-invention is to provide secondary. clock apparatusof the type referredto which isoi' improved construction Vandarrangemerit of parts. y

A further' object of the invention is to provide a secondary clock of the minute impulse type; which is extremely quiet'in its operation, suchquietness of operation being eifected by virtue of certain counterbalancing spring biasing means employed in connection with the present invention.I

' A'still further object is to provide secondary clock apparatus of the impulse type which is composed of relativelyv few parts and which is relatively low in cost.

A further object is to provide an impulse type secondary clock which has an improved construction'and arrangement of magnet coil and armature-and which may be operated either by an A. C. or a D. C. signal impulse.

A still further object is to provide a secondary clock having an annular coil and an oscillating armature disposedwithin said coil and' which ispreferred form of secondary clock apparams conl structed in accordance with the present invention;

' Fig. 2 is a vertical section taken on the line Fig. 3 is a fragmentary vertical sectional view taken on the imei-Icing. 2 with the annular magnet coll omitted but e outline thereof being indicated byV the dot-anddash lines. the view showing the normal ornon-energized position of the armature;

Fig. 4. is a fragmentary vertical section taken on the same-plane. as' Fig. 3 and showing the armature in its energized or attracted position; v

and

Fig. 5 is va fragmentary horizontal section show- 1g.. ing in plan the meehanismfor transmitting the motion of thearmature to the time indicating shaft.

Referring now in detail to the construction illustrated. the reference numeral II indicates a example. as a moldedfinsulatingmaterial. As shown, the housing is-shapedV substantially as a drum and comprises acircular front wall il, a

'20 rear wall 1 2, and a cylindrical side wall i3. In

25 by any suitable means such, for example, as

screws It'. The screws I4 extend through an opening I5 in the rear part ib andengage a threaded opening i6 the front part Illa; The

-. front part ita is 'formed with outwardly extendso ius supporting ears li g5 shown).

A having openings formed therein. In each 'of these openings is mounted a rubber grommet il through which is adapted to extend the means for securing the housing il within the-conventional clock casing (not 11tlrits casing and thereby Qperating noises.

The front halt lla of the housing includes the aid in reducing clock 40 circular end wall ii which is provided with an opening 2l through the center thereof. As shown.

. nism within the 'housing il, and is also formedy 59 with a terminal mounting block 22 on -the lower the front half i3d of the cylindrical side wall Il is joined to the periphery of the end wall Il and is formed as a continuation of the rear half i3b 4 5 of the vcylindrical side wall which is formed on the rear halfilb of the casing. The rear end wall I2 is formedwith an opening 2i in the upper part thereof to permit access to the clock mechalglclock supporting housing which may be formed of any., suitable non-magnetic material such, for

The rubber grommets minimize the# transmission of vibrations from the clock housing part thereof which serves as a means for holding terminal straps for making electrical connections.

A bearing sleeve 23 is fixed at one end thereof within the centralopening in the front end wall Il and the sleeve 23 extends rearwardly coaxially within the housing as shown in Fig. 2. A minutes shaft 24 is journalled within the central bore of the sleeve 23 and extends forwardly beyond the front end wall Il and the conventional minutes hand 25 is secured to the outer forward end thereof.

Arranged' concentrically within thev drumshaped housing I0 and supported from the cylindrical side wall I3 thereof, `is a hollow annular supporting member 26, in which is disposed an wound in the conventional manner on a mounting ring 28 of suitable insulating material. The two terminal wires 30 and 3| of the coil are shown in Fig. l as attached, respectively, to terminal straps 32 and 33 carried by the mounting block As shown in Fig. 2, the annular supporting member 26- is channel or U-shaped in cross section with the open side of the U at the'inner cir-- cumference thereof. The member 26 is formed of a suitable permeable material; and, in order to facilitate manufacture and assembly, is divided along a median transverse plane into symmetrical halves 26a and 26h, respectively. The halves are formed with abuttingflanges 35a and 35h, respectively, which extend radially outward from the outer circumferential wall thereof and are disposed between the front Aand. rear halves Illa and Illb of the housing I8. The flanges 35a and l351) are provided with aligned openings 36 through which the housing securing screws I4 extend. Thus, the screws I4 serve as a means for detachably securing together two halves of the housing I0 and the two halves of the annular 40 supporting member 26 and as a means for holding the supporting member 26 in its proper concentric relation with respect to the axis of the housing I0. 4

The annular supporting member 26 includes a plurality of circumferentially spaced pairs 38 of pole pieces, the pole pieces of each pair 38 being indicated, respectively, by the reference numerals 38a and 38h. The pole pieces 38a and 38h ofeach pair are formed integral with the two opposite sides of the member 26 and they extend inwardly toward one another across the open inner side of the channel-shaped supporting member and terminate short of one another to provide an air gap therebetween. As shown in Fig. 3, there are nine pairs 38 of pole pieces provided. The ringshaped strip 28 of insulating material in conjunction with the pairs of pole pieces38a and 38h, serve to hold the coil 21 within the supporting member 26.

An oscillating armature 40 is journalled on the axially disposed supporting sleeve 23 and comprises a central hub 4l mounted-en the sleeve 23,

. and a disk-like web 42 fixed at its center to the hub and extending radially outwardly from the latter and terminating at its periphery in a circular rim 43 from which extends a plurality of separate flanges 44. The rim 43 and flanges 44 are madefof a suitable permeable material and the flanges form armature elements which coact with the pairs 38 of pole pieces of the supporting member 26. The flanges are spaced circumferentially about the rim 43 and correspond in number and spacing to the pairs 38 of pole pieces. The arrangement of the flanges is such that when i5 annular magnet coil 21. The coil 21 is circularly 4 the magnet coil 21 is energized, the resulting magnetic force moves the flanges 44 circumferentially into bridging relation 'with respect to their corresponding pairs 38 of pole pieces 38a and 38h and thereby rotates the armature 4I from its normal or non-energized position shown in Fig. 3 to its energized position shown in Fig. 4.

Biasing means is provided for constantly urging the armature 40 to rotate in a. direction opposite to the magnetic force of the coil and back to its normal or non-energized position. This biasing means advantageously comprises a weight 46 fixed 'to the outer end of a spring 41, the inner end oi the spring being wound spirally around and anchored to the hub 4l of the amature 40. In order to dampen vibratory movements of the "weight 46, a leaf spring 43 is xed at one end to the web 42 of the armature and the other or outer end thereof lightly engages the side of the weight'46.

A resilient stop device is provided for stopping movement of the armature at its normal or nonenergized position when the armature is moved -from its energized position by the force of the weight 46. The weight 46, in conjunction with the stop device, willl then hold the armature at its normal or non-energized position. This resilient stop device is shown as comprising a leaf spring 50 anchored to posts 5I and 52 which extend in- 30 wardly from the end wall Il of the housing Il and through a cut-out opening 53 in the web 42. As shown in Fig. 3, the spring 5l extends downward from the post 52 and into the path of movement of one of the amature flanges 44, the latter striking the lower end of the spring 5l and being held against the spring by the weight 46 to determine the non-energized position of the armature 4l.

In accordance with the present invention, a motion-transmitting means is provided in the illustrative embodiment which functions to convert the oscillatory movement of the armature 4I between its energized and non-energized` positions into intermittent time-keeping rotation of the minutesshaft 24. This means comprises a pawland-ratchet mechanism driving a train of gears with the last gear of the train being fixed to the minutes shaft. As shown in Figs. 2, 3, 4, and 5,

a four-tooth ratchet wheel 55 is mounted for 50 rotation about a xed stud 56 projecting inwardly of the housing from the end wall Il thereof and through a cut-out opening 51 in the web 42 of the armature. Coacting with the ratchet 55 is a pawl 58 pivotally mounted on a pin 53 extending 55 from the rim 43 of the armature 46. 'I'he pawl is biased toward a. stop. flange 6| formed on the rim 43 by a suitable spring 66. The construction and arrangement is such that when the armature is rotated due to the energizing of the coil 21 from 30 its normal position of Figs. 3 and 5 to its energized position of Fig. 4, the pawl 58 is carried back over one tooth of the ratchet wheel 55. When the coil is deenergizcd, the weight 46 rotates the armature back to its normal position of o5 Figs. 3 and 5, and in so doing, the pawl 58 engages a tooth of the ratchet wheel 55 and thereby advances the ratchet wheel counterclockwise, as viewed in Figs. 3 and 4, one increment of rotary movement. At the end of this advancing stroke.

the pawl` 58 overlies the next tooth of the ratchet wheel and thereby prevents overthrow movement of the ratchet and also holds the latter at the advanced position. As shown in Fig. 5, a plate 62 is pivoted to the rim 43 of the armature 48 .15 and is formed with an outwardly extending oiset endportion i9 whichisshapedsoastoforma continuation of the pawl Il. When the amature is rotated to its energized position of Fig. 4, the offset portion 63 of the plate 92 follows the pawl 59 and at the end of such movement the portion i3 overlies two teeth of the ratchet wheel and thereby locks the latter against movement in either direction. As the pawl 5I moves on an advancing stroke, the offset end portion 63 leads the pawl and releases the ratchet wheel for movement before it is engaged by the pawl.

As shown more clearly in Figs. '1, 2, and 5, a driving pinion is formed integral with the ratchet wheel 55, and the pinion 95 mhes with a gear ii mounted for rotation on a stud I1 xed totheendwall ofthehousingandalsoextending through the opening 51 in the web l2. A pinion gear Il is fixed coneentrlcally to the side of the gear i6 andmeshes withalargegear il which is suitably fixed to the minutes shaft 24. AsshowninFigs.3and4,thesideofthegear It is formed with radially disposed ratchet teeth 1I which are adapted to be engaged by the outer free end of a leaf spring detent 1|, the latter being fixed at its other end to a stud 12 projecting inwardly from the end wall il and through a cut-out opening 19 in the armature ll. As will be apparent, the spring detent 1| coacts with the teeth 1I to prevent retrograde movement of .the gears and ratchet.

It will thus be seen that as the magnet coil 21 is energized and then deenergined, the armature moves from its normal position to its energized position and then back to its normal position and in so doing the increment of movement imparted to the ratchet wheel I5 by the pawl 59 is transmitted by the gearing just described to the minutes indicating shaft 2l. As a result, the shaft 24 is rotated a predetermined angular distance in a time-keeping direction. As is well known to those skilled in this art, energizing impulses are transmitted to secondary clocks. under the control of a master clock (not shown), once each minute and as a result the minutes hand of each secondary clock is advanced an angular distance equal to one minute.

In accordance with the present invention, a novel means is incorporated in the secondary clock, which functions to drive an hours indicating member from the minutes indicating member. As shown more clearly in Fig. 2, the hours hand 15 is fixed to a sleeve 1i frictionally molmtved on ahub 11 whichis,inturn,journalledona sleeve 19 that rotates with the minutes shaft 2|. The intermittent rotary motion of the minutes shaft 2listransmittedtothehourshand1i-for advancing the latter its proportionate amount, by means 'of a planetary gear train which comprises a pinion ll fixedtotheminutesshaftu, a stationary ring gear 9| flxedwithin a circular depression in the forward face of the end wall of the housing Il gear teeth I2, and a planetary gear 93 meshing both with the teeth of the pinion 8l and also with the teeth of the ring gear 8| and moimted for rotation on a stud I4 carried by the outer end of a planet arm 85, the latter being fixed at its inner endtothehub11carryingthehourshand. Thus, as the minutes shaft is advanced, the just described simple form of planetary gearing advances the hours hand at its proportionate rate.

As stated hereinabove, the timekeeping apparatus of the'present invention is designed for use asacontrolledsecondaryelement of anautomaticclocksystemlike 6 that disclosed in Bryce U. S. Patent No. 1,687,491. In such a system, certain contacts are provided in the secondary which control the reception of time signals from the master clock in accordance with the time-indicating position of the secondary.

In the illustrative embodiment, the terminal gear 69 of the clock driving train is advantageously composed of a suitable molded insulating material, and the rear face thereof is shaped as a cam surface 91, which functions to operate contacts according to the time-indicating position of the secondary. As shown, in Fig. 1, the terminal strap 32 previously mentioned, and additional terminal straps ll and 89 are secured to the block 22 and are constructed with inwardly extending spring extensions 90, 9| and 92, respectively. A contact point 93 is formed on the extension 9| which is adapted to engage the extension 99 and the latter is formed with a contact point 94 adapted to engage the extension 92. The spring extension 9| is biased toward the intermediate extension and the spring extension 92 is biased away from the intermediate extension l99. The outermost end 95 of the spring extension 92 engages the cam face 91 adjacent the outer periphery thereof and the outermost end 96 of the intermediate extension 99 engages the cam -face 91 at points spaced radially. inward of the end 95. The outermost end of the extension 9| carries a spacing pin 91 of insulating material which is adapted to engage the extension 92. The shape of the cam surface Il is on the order of a helix with the axis of the gear i9 as the center. As will be noted from an examination of Figs. 1 and 2, the height of the cam surface 81 is the same along any given ra.- dial line, except. at the high point of the cam surface where the outer portion engaged by extension 92 terminates at a drop-off point 99 and the inner portion terminates at a drop-olf point 99 angularly spaced from the point 98. Thus, for any portion of the cam surface, 81, except the angular space between the points 98 and 99, the

. innermost ends 95 and 99 of extensions 92 and 99, respectively, engage cam surfaces of the same height and the contact point 94 engages and thereby provides electrical contact `between extensions 90 and 92 andthe spacing pin 91 engaging the extension 92 holds the extension 9| and its contact points A93 out of electrical contact with the intermediate extension 99. As the clock advances, the cam surface 81 rotates in the'direction of the arrow, Fig. 1. Thus, the end 95 of the extension 92 reaches its drop-off pointl 99 while the end 9G of extension 90 is still engaging a high part of the cam surface. As the end 95 of extension 92 drops o the high point 98, it breaks the electrical connection with the intermediate extension 90, and permits the contact point 99 on extension 9| to move with the latter and into electrical engagement with the extension 99. It will be apparent that the foregoing provides a simple, effective and inexpensive form of contact construction and actuating means therefor.

The strap 99 is connected to the A wire of the Bryce synchronizing clock system disclosed in Patent No. 1,687,491, referred to above; the strap 99 is connected to the B wire of the clock system; the strap 32 is connected to one end of the magnet coil 21 by the Wire 30; and the strap I3, which is connected by the wire 3| to the other end of the magnet coil 21, is also connected to the C or ground wire of the Bryce clock system.

As is fully` disclosed in the Bryce patent referred to, the clock advancing signals are transmitted each minute over both the A and B wires from the sixtieth minute of the master clock to the beginning of the synchronizing period which nects the B wire to the magnet coil. Thus, if

the secondary is on time, the rapid impulses over the A wire during the fty-ninth minute will not be transmitted to the coil 2l and the latter will receive the sixtieth minute impulse over the B wire. The drop-ofi 89 is spaced angularly from point 98 about ten minutes so that at about ten minutes past each hour, extensions 90 and I2 will again engage the cam surface 91 at equal heights and impulses over the A wire will again be transmitted to the magnet coil.

While there have been shown and described and pointed out the fundamental novel features of the invention, as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form -and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a secondary clock of the electrical impulse type, the combination of an annular magnet coil arranged with its axis approximately horizontal; a plurality of pairs of pole elements arranged in spaced relation circumferentially around said coil; an oscillatory armature mounted for rotary movement about the axis of said coil and including a plurality of circumferentially spaced armature elements corresponding in number and spacing to said pairs of pole elements and being arranged so that upon energization of said coil the resulting magnetic force moves said armature elements circumferentially and into bridging relation with respect to corresponding pairs of pole elements and thereby effects rotation of said armature from a retracted position to an advanced position; a torque-applying weight; means resiliently securing said weight to said armature in a position when the armature approaches its retracted posioutwardly from the axis of rotation of the armature whereby the mass of said weight, by the force of gravity, constantly applies a torque to said armature tending to restore the same to its retracted position; a resilient abutment positioned in the path of movement of the armature and designed for engagement with the latter when the armature approaches its retracted position; said resilient securing means and resilient abutment counterbalancing each other when the armature is in its retracted position and together determining the fully retracted position of the armature; a time indicating element; and motion-transmitting means actuated by movement of said armature from its retracted to its advanced position for advancing said time indicating element.

2. In a secondary clock of the type adapted to be advanced by regularly spaced electrical impulses the combination of a drum-shaped housing including a circular end wall and a cylindrical side wall joined to the periphery of the end wall; a bearing sleeve arranged axially of the lhousing and extending through the center of said end wall; a time indicating shaft journalled within said sleeve; a hollow coil-supporting ring arranged coaxially within said housing and about the inner periphery of the side wall thereof and being secured to the latter and said ring having an open inner periphery and being formed of permeable material and including a plurality of pairs of pole pieces arranged in spaced relation about the inner circumference of the.

ring and the pole pieces of each pair extending inwardly toward one another from opposite sides of the ring and terminating short of one another to provide an air gap therebetween; an annular magnet coil concentrically disposed within said ring; an oscillating armature comprising a hub journalled on said bearing sleeve, a disk-like web extending radially from the hub and including an annular outer rim, and a. plurality of armature elements formed of permeable material and extending, respectively, from the outer rim in directions parallel to the rotary axis and being spaced from one another about an imaginary circle concentric with the rotary axis, the armature elements corresponding in number and spacing to said pairs of pol pieces and being so arranged that upon energzation 0f said coll the resulting magnetic force moves said armature elements circumferentially into bridging relation with respect to corresponding pairs of pole pieces and thereby effects rotation of said armature from a normal or non-energized position to an energized position; biasing means constantly urging the armaturev to rotate in a direction opposed to the magnetic force and towards its said normal position; a stop device secured to said housing and adapted to be engaged by and to stop rotation by said biasing means at said normal position; and motion-transmitting means actuated by movement of said armature between its said energized and non-energized positions and operable, when so actuated. to advance said time shaft one increment of movement. f

3. In a secondary clock of the type adapted to be advanced by regularly spaced electrical impulses the combination of a drum-shaped housing including a circular end wall and a, cylindrical side wall joined to the periphery of the end wall; a bearing sleeve arranged axially of the housing and extending through the center of said end wail; a time-indicating shaft journalled within said sleeve; a hollow coil-supporting ring arranged coaxially within said4` housing and about the inner periphery of the side Wall thereof and being secured to the latter and said ring having an open inner periphery and being formed of permeable material and including a plurality of pairs of pole pieces arranged in spaced relation about the inner circumference of the ring and the pole pieces of each pair extending inwardly toward one another from opposite sides of the ring and terminating short of one another to provide an air gap therebetween; an annular magnet coil concentrically disposed within said ring; an oscillating armature comprising a hub journalled on said bearing sleeve, a disk-like web extending radially from the hub and including an annular outer rim, and a plurality of armature elements formed of permeable material and extending, respectively, from the outer rim in directions parallel to the rotary axis and being spaced from one another about an imaginary circle concentric with the rotary axis, the armature elements corresponding in-number and spacing to said pairs of pole pieces and being so arranged that upon energization of said coil the resulting magnetic force moves said armature elements circumferentially into bridging relation with respect to corresponding pairs of pole pieces and thereby effects rotation of said armature i'rom a, normal or non-energized position to an enrgized pomtion; a weight resiliently secured to said amature at points spaced laterally from the rotary axis thereof and so as to constantly urge the armature to rotate in a direction opposed to the magnetic force and towards its said normal position; a resilient stop device secured to said housing and adapted to be engaged by and to stop rotation of the armature by said weight at said normal pomtion; a ratchet supported by said housing and mounted to rotate about a fixed axis; a pawl pivoted on said armature and coacting with said ratchet to rotate the latter one increment of movement upon movement of said armature between its normal and energized positions; and gearing means for transmitting motion from said ratchet to said time shaft.

4. In a secondary clockof the electrical impulse type, the combination of an annular magnet coil arranged with its -axis approximately horizontal; a plurality oi.' pairs of pole elements arranged in spaced relation circumferentially around said coil; an oscillatory armature mounted for rotary movement about the axis of said coil and including a plurality of circumferentially spaced armature elements corresponding in number and spacing to said pairs of pole elements and being arranged so that upon energization of said coil the resulting magnetic force moves said armature elements circumferentially and into bridging relation with respect to corresponding pairs of pole elements and thereby eiects rotation of said armature from a retracted position to an advanced position; a torque-applying weight; means resiliently securing said weight to said armature in a position whereinits center of mass is spaced radially outwardly from the axis of rotation of the amature whereby the mass of said weight, by the force o! gravity,- constantly applies a torque to said armature tending to restore the same to its retracted position; a resilient abutment positioned in the path of movement of the armature and designed for engagement with the latter when the armature approaches its retracted position; said resilient securing means and resilient abutment counterbalancing each other when `the amature is in its retracted position and together determining the fully retracted position of the armature; a time indicating element; a spring element frictionally bearing against said weight and serving to dampen the inherent oscillatory movements of the latter as the armature reaches either of its limiting positions; and motion-transmitting means actuated by movement of said armature from its retracted to its advanced position for advancing said time indicating element.

5. In a secondary clock of the electrical impulse type, the combination of a magnet coil having a substantially horizontal axis; a plurality of pairs of pole elements arranged in spaced relationship circumferentially around said coil; an oscillatablearmature mounted for rotary movement about the axis of said coil and including a plurality of circumferentially spaced armature elements corresponding in number and spacing to said pairs of pole elements and being arranged so that upon energization of the coil the resulting magnetic force moves the armature element circumferentially and into bridging relation with respect to corresponding pairs of pole elements to thereby eiIect rotation of the armature from a retracted position to an advanced position; means normally biasing said armature in a, direction opposite to the direction eiected by said magnetic force whereby said armature is normally urged toward its retracted position; a ratchet wheel mounted for rotation about 9, fixed axis and occupying a position adjacent the periphery of said armature; a pawl mounted on said armature adjacent the periphery thereof; said ratchet being formed with a series of teeth thereon, one of which normally projects into the path of movement of said pawl as the latter moves with the armature from its retracted to its advanced position, said pawl occupying a position when the armature is in its advanced position wherein it bridges two adjacent teeth on the ratchet wheel and prevents either overthrow or return movement of the ratchet wheel; a finger mounted on said armature and occupying a position wherein when the armature is in its attracted position it overlies two adjacent teeth on said ratchet wheel and locks the latter against movement in either direction; a time indicating element; and means operatively connecting said ratchet wheel and said time indicating element in driving relationship.

6. In a secondary clock of the electrical impulse type, the combination of an annular magnet coil having a, substantiallyhorizontal axis; a plurality of pairs of pole elements arranged in spaced relationship circumferentially around said coil; a spider-like oscillatable armature having web portions with openings existing therebetween mounted for rotary movement about the axis of said coil and including a plurality of circumferentially spaced amature elements correspond- Ying in number and spacing to said pairs of pole elements and being arranged so that upon energization of the coil the resulting magnetic force moves said armature circumferentially into bridging relationship with respect to corresponding pairs of pole elements and thereby effects movement of the armature from a retracted position to an advanced position; means normally biasing said armature to its retracted position; a time indicating element; motion-transmitting means actuated by movement of the armature from its retracted to its advanced position to advance said time indicating element, said motion-transmitting means including a ratchet wheel mounted for rotation about a iixed axis parallel to the axis oi.' rotation of said armature, said ratchet wheel occupying a position within one of vthe openings existing between said web portions, the periphery of said ratchet wheel being positioned close to the periphery of said armature; a pawl mounted on said armature adjacent the periphery thereof and operable upon movement of the armature from its retracted to its advanced position to engage a, tooth on said ratchet wheel and impart an increment of motion to the latter, said pawl when the armature is in its advanced position bearing against a, pair of adjacent teeth on the ratchet wheel and preventf ing overthrow or retrograde movement of the ratchet wheel; and a linger mounted on said amature adjacent the periphery thereofy and positioned relative to said pawl whereby when said amature moves to its attracted position the nger engages the pair of teeth released by said pawl to lock said ratchet wheel against movement in either direction.

. RIYNOLD B. JOHNSON.

EDWARD I'. GEIGER.

REFERENCES CITED The following references are o! record in the me or this patent:

Certificate of Correction Patent No. 2,510,583

REYNOLD B. JOHNSON ET AL.

It is hereby certified that errors appear in the printed specication'of the above numbered patent requiring correction as follows:

Column 7, line 59, strike out when the armature approaches its and insert instead wherein 'its center of mass is spaced radially;

retracted posi and that the said Letters Patent should be read With these corrections therein tha.

the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of September, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommssz'oner of Patents. 

